clk: socfpga: update clk.h so for Arria10 platform to use

There are 5 possible parent clocks for the SoCFPGA Arria10. Move the define
SYSMGR_SDMMC_CTRL_SET and streq() to clk.h so that the Arria clock driver
can use.

Signed-off-by: Dinh Nguyen <dinguyen@opensource.altera.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>